What kinds of perceptual organization can occur without awareness of the stimulus? Previous studies addressing this issue yielded inconsistent results (e.g., Harris et al., 2011; Lau & Cheung, 2012; Montoro et al., 2014; Moors et al., 2015; Wang et al., 2012). The inconsistency may be partly due to different techniques used to induce invisibility. In this study, we examined whether visual consciousness is required for two perceptual grouping principles: luminance similarity and element connectedness, using priming paradigm and the same technique — continuous flash suppression (CFS; Tsuchiya & Koch, 2005) — to render the prime invisible. Participants were presented with a liminal prime consisted of dots organized into rows or columns by luminance similarity (Experiment 1; 20 participants) or by element connectedness (Experiment 2; 19 participants), followed by a clearly visible target composed of lines, the orientation of which could be congruent or incongruent with the orientation of the prime. The prime-target SOA varied (200,400, 600, or 800 ms). On each trial participants made speeded discrimination response to the orientation of the target lines (vertical or horizontal) and then rated the visibility of the prime using a scale ranging from 0 ("I saw nothing") to 3 ("I clearly saw …"). Unconscious grouping of the prime was measured as the priming effect on target discrimination performance of prime-target orientation congruency, on trials in which participants reported no visibility of the prime. In both experiments, and across all prime-target SOA, there were no priming when the prime was reported invisible; significant priming was observed when the prime was reported visible. These findings suggest that perceptual grouping by luminance similarity and by element connectedness does not take place when the visual stimulus is rendered nonconscious using CFS.